The demand for miniaturizing electrical assemblies requires devising techniques to efficiently utilize the available area on a main circuit board. A so-called flip-chip technology has been utilized, wherein a bumped integrated circuit (bumped IC) carries a pad arrangement on its front surface. The IC is turned upside down, i.e. flipped, allowing direct coupling between the pads and corresponding contacts on a main circuit board or a chip carrier. The direct connection is facilitated by forming solder or gold bumps on the IC's input and/or output terminals. Accordingly, the flipped IC chip is referred to as a flip-chip. During manufacturing, the flip-chip is aligned to the chip carrier and all connections are made simultaneously by reflowing the solder. The flip-chip technology, therefore, allows for direct interconnecting pads of an integrated circuit (IC) chip to corresponding contacts on the main circuit board.
Another and more conventional method by which terminals of an IC chip are connected to contacts of the circuit board or the chip carrier is wirebonding. In a wirebonded IC chip, an upwardly-facing chip is placed on a circuit substrate such that its input and/or output terminals are exposed. An array of wires connect these terminals to corresponding contacts on the circuit substrate. The wires connect the terminal to the contacts using well-known wirebonding or tape-automated bonding techniques.
As a result of increasing complexity of large scale integrated circuit chips, a larger area or real estate is required for packaging the IC chip. Generally, one or more IC chips are electrically coupled to each other in order to make the electronic device functional. For example, a microprocessor and a number of memory devices may be electrically coupled to each other in order to provide operational control for the electronic device. Conventionally, the microprocessor chip and the memory chips are positioned next to each other on one surface or on opposing surfaces of a main circuit board which includes a substantially large number of components. The terminals of the IC chips are coupled to each other by means of circuitry disposed on or within the circuit board. This approach, however, consumes substantial real estate because the area required for positioning each IC chip must be accommodated for on the circuit board.
In order to enhance real estate utilization, stacked integrated circuit chip arrangements are conventionally used. In such arrangements, two or more IC chips are stacked on top of each other. In the conventional stacked arrangement, however, all of the IC chips are either faced downwardly, upwardly, or side by side, wherein all face in one direction. This arrangement, however, makes the interconnection among their terminals and external circuitry substantially difficult and complex. Therefore, it is desired to position two or more chips on a circuit board without consuming a lot of real estate while providing simple interconnections between the terminals of the IC chips and the external circuitry.